High potential current transformer means



24, i943 A. c. @CHW/GER HIGH POTENTIAL CURRENT TRNSFORMER MEANS Filed Dec. 2l, 1942 Vm f) dem Ao. $911. -Own ..MX faQ?. :f 5 9 5% no l parable current Patented Dec. 24, 1946 HIGH POTENTIAL CURRENT TRANS- FORMER MEANS lAugust C. Schwager, Miilbrae, Calif., assignor to Pacific Electric Manufacturing C Francisco, Calif., a corporation of Calia San forni orporation,

Application December 21, 1942, Serial Nia-469,613

Claims. (Cl. 175-358) My present invention relates t0 high potential current transformer means, and more particularly to an improved current transformer and system for use in connection with the operation of control apparatus responsive to current con- 1titions upon a high potential power transmission ne. v

An object of the invention is to provide a current transformer of new and novel design for high potential heavy current power transmission lines which will be practical, efficient and more economical to manufacture than would be a comtransformer for use under the same conditions of operation.

Another object of the invention is to provide a new and novel current transformer of small size and simple construction in which an evacuated spacing between the primary and secondary windings is relied upon as a means to insulate the high potential primary winding from a secondary operates at a substantially lower and safe voltage at ground potential.

Another object of the invention is to provide a current transformer that is particularly well adapted for use in connection with the so-called minimum oil" and "air blast types of high voltage circuit interrupter which operate in a zone of high potential and consequently do not require the conventional insulating bushings within which the current transformers of former design were customarily mounted.

Another object of the invention is to provide a transformer system for effecting an insulated current responsive control connection between a high potential power transmission line and a control circuit in which a current condition responsive to current conditions upon the high potential transmission line is inductively transmitted through an insulating vacuum to a control circuit operating at a. safe grounded potential.

-In the art to which the invention relates, current transformers are relied upon to provide a measure of the current flowing in a. high voltage alternating current system and/or to provide a source of current for a system of control having relays and other instruments operating at a considerably lower potential.. In the past, where these current transformers have been associated with extremely high voltage circuits, it has been the custom to mount the current transformer in the insulating bushingsy generally provided with the terminals of circuit breakers and like apparatus to insulate the apparatus operating at ground potential from the high potential circuit.

However, due to recent trends, and particularly tank for its windings. For exampl to developments in the so-called minimum oil circuit breakers and air blast circuit breakers which have their operating and circuit interrupting elements mounted and operating in the zone of high potential, the aforementioned insulating bushings have become unnecessary. Therefore, a different form of current transformer must be provided to meet this condition. Due to the high voltages involved, the cost of an independent transformer makes its use almost prohibitive, as such a transformer must still be provided with a large insulating bushing and an oil containing lthe primar-y current of these transformers is generally somewhere in the neighborhood of 600 amperes and, therefore, heavy conductors of approximately one square inch of cross-section must be used for the primary winding. The secondary winding of these transformers is usually designed for approximately five amperes and, consequently, av very small wire can be used for this winding. However, in order to prevent electrical break down between Vthe primary winding and the core and the secondary winding of such a transformer, a large insulating space must be provided, and while this spacing is somewhat reduced when an oil or other insulating medium is used, the distance between theprimary winding and the core must still remain relatively large in order to insure sufficient safety. This distance must be somewhere in the neighborhood of ten inches on a 115,000 volt circuit.

It has also been recognized that air under high pressure breaks down under electrical stress less easily than air at atmospheric pressure, and recently, as a solution to the above problem, it has been proposed to insulate the core and windings of a transformer by placing them in a, suitable container under high air pressure. 'I'his will reduce the required spacing or clearance distance between the primary and secondary windings and the core of the transformer. While these transformers have the advantage that they avoid the fire hazard inherent in the use of an inflammable insulating oil, they still have the disadvantage that extra precautions must be taken to insure that the high air pressure surrounding the windings of the transformer is maintained at all times.

In accordance with the present invention and as distinguished from the above prior art practices, I propose to seal the entire transformer unit Within a glass or other form of envelope from which the air is completely exhausted and use a high vacuum as the insulating medium between the primary and secondary windings and the core rI3 of the evacuated glass v rangement it will' be seen that the turns ornconi is.one which might be connected directly to power transmission line with its primary ,Y carrying the full line current. However,V

so that an evacuated space will be interposed between'the two windings and/orbetween atleast one of the windings of the transformer and the core. In this manner the spacing between the transformer windings and the core and the spacing between the two windings can be reduced to a, minimum and, at the same time, a maximum factor of insulating safety will be provided.

In accordance with another aspect of the in-'f more transformers 4 since it is appreciated that there may be limitations in the size or character of the lead in conductors I4 and I 5 that would preclude or make difficult the sealing of such conductors in the wall of anevacuated-container, it is contemplated that resort may be had to the use of la conventional current transformer for the purpose of providing a. current ofreduced value that can be accommodated by lead in conductors of a size suitable for sealing in the wall of an evacuated container.

In Figure 2v of the drawing there is shown an embodimentof the invention inwhich both the For a better understanding of the invention y reference should'be had to the accompanying drawing, wherein there Yis shown byrway of illustration and not of limitation preferred embodiments thereof. A

In the drawing: I Figure 1 is a diagrammatic sectional view showing one form of my invention,

Figure 2 is a similar view illustrating another form ofmy invention as connected inr series with a current transformer of conventional design, andV Figure 3 is a vertical sectional vview showing 'an adaptation of my invention "suitable for use in connection with minimum oil and air blast types of circuit breakers. v f y In Figure 1 of the drawing the invention is shown in simplified form as employing a suitable evacuated glass bulb or rece'ptacieill in which the transformer is enclosed and sealed as a unit. ',Ihe glass bulb Ill has an-enlarged central body portion II from which reduced end portions I2 and/I3 extend in' opposite directions. Sealed in and passing through the extending end vportion I2 of the bulb I0 there are two, relatively largecon- I ductors I4 and I5 whichprovide lead in lconnections for a lrelatively small number of ampere turn forming convolutions I6 of .the same conductor which form the primary windingvof a transformer. Positioned within the enlarged portion Il of the bulb I0 by means Aof suitable supports I'I and with one of its legs extendingcentrally through the convolutions I6 of the lprimary winding, there is a magnetic core I8 of suitable construction. This magnetic core I8 is shown as of rectangular shape` and upon the .other ofits legs and, wound in a suitably insulated manner, there lis a secondary winding I9 having lead out .wires 20 and 2 IthatV are sealed in and extend outof the extending neck bulb III. With thlsarwardly through the end volutions AI 6 of the primary w'nding willbe'spaced from the core .I Bof the transformer .ati'id'thus providean evacuated space between this windingand .the core I8v that will effectively insulate the 'turns I6 of the primary winding from the corel I8.A it` the same time, by extending the n'eclrsk l2 and I3 upon the bulb Ill'outwardly a vsafe distance, depending uponthe voltage involved, the terminal 'primarywinding and lthe secondary winding of my high potential insulating current transformer are each spaced from the magnetic core and insulated from `the core and from each other by a high vacuum. vAs here shown, the transformer is enclosed within an elongated and evacuated bulb .'22 having an extending neck 23 at one end in which primary current leads 24 and 25 are sealed. .These vcurrent leads 24 and 25 form the input conductors of a primary winding 26 that is suitablyrnountedv within the bulb 22 by means of a reentrant stem `21 formed within the bulb 22. At its other end the bulb 22 has an oppositely extending neck 28 in which 'lead out conductors 23 and 30 are sealed. These latter conductors 23 and 30 form the output conductors of a secondary winding'l which, like the primary winding 26, is suitably supported within the bulb 22 by means of a second reentrant stem 32. With this arrangement it lwill be seen that the primary winding 2li and the secondary winding 3| will be spaced and insulated from each other. To complete an inductive coupling between the primary lwinding 26 and the secondary winding 3I the bulb 22 is shown as vhaving a substantially centrally disposed magnetic core 33 that is positioned by'means of supports 34'with its opposite legs disposed in spaced and substantially central relation with respect to the convolutions ofthe primary andfsecondary windings. In this transformer it is contemplated that the ratio of turns ofthe primary winding 26 and the secondary winding 3| will be substantially 1:1. However, it is conceivable that this ratio of transformation may'v be of any desired value,either'in a step-up or step-down sense. In practice, it is customary to provide transformers for this service which have a secondary current output of approximately five amp'eres., as this value of current' is very' satisfactory for'meters and relay control circuits. Therefore, as illustrated'in this gure of the drawing; my improved transformer is shown as connected in series with Va transformer of conventional design which has a heavy current carrying primary windingv 35 and a secondary winding 36 that will' provide a control current of sub- Y stantially ve ampereswhenV the normal line cutrent is iiowing through its primary winding.

v'In Figure 3 of thedrawingthere is shown 'an Aembodiment of the invention'which it is believed may find considerable useinvr connection with the potential insulating bushings such as are nowreends of the conductors I4', l5'and 2.0,r 2lvmay be spaced apart suiicentlyf'to avoid any external arc-over. around the `vacuum insulated gap between the primary and secondarywindings of the transformer'.` The transformer described above a high potential winding type.

quired on circuit breakersfof the oil insulated As here shoWrrthe insulating transformer iis enclosed within an evacuated glass bulb orenvelope 31. The insulating transformer in this instancelcomprises a magnetic core 38 that is posiftion'ed within the bulb 31'bys`uitable'supports 39 and 40. The core. 38"carries a secondary winding 4I having leads 42 and 43 that extend through and l are sealed in the wall of the bul'bg31 nearits botto`m. At Vits upper end the bulb 31 yis provided with a neck of reduced vdiameter having a 'reentrant stem 44 upon which there` is suitably m'ounteda primary winding 45. yThis primary winding 45 has relatively large'convoluti'on's 45 that surround'and are disposed in spacedre'lat'ion with the upper legoi tliemagnetic coref38. iExtending adjacent the reentrant vstern 44 'there-'are two lea'dsin Aconductors '41 `and '48 vthat extend through andare sealedin the end of the'upwa'rdly extending 'neck of'tlie bulb 31. VIn this arrangement, like that illustratedin connection with Figure 2, Ythe insulating transformer isfadap'te'd'tobe connectedvin series with a vtransformer of iconventional design, and in order to provide for'the support and insulation of 'this conventional transformer, the bulb 31 is shown as disposedcen'trally within a bushing-type insulator 4,9 o'f'porcelain or other suitable material. chanical and insulating -support'for the conventional current transformer. Theinsulatingbushing 49 has a plate 50 upon which 'a 'core 45| of the conventional transformer is supported. The core 5i of this latter transformer has a,V primary winding 52 anda secondary vwinding 53 that may be designed to provide -a control current of any Idevsired value, as will be determined by'the normal current of the lineconductor in Vwhichthe pri-mary vwinding-52 of this transformermay be connected.

Terminals 54 and 55 carried by the primary'wind- -ing 52 are here shown as insulated, froml and :pro-

Jecting through' an enclosing cover 56 that'is likewise insulated and supported in ythe zone vof high `potential at the upper end of-thebushing 49. In connection with vthis latter arrangement, it will be noted that the first stage or conventionall transformer, together with its enclosing'housing 56 and the power line conductorsl connected to theterminals 54 and 55 of the primary Windingf52, will be eiTectively insulated from ground by meansof the supporting insulator bushing 49. fNow, in order to further insulate the high potentiaicircuit and reduce thepossibilityof any creepage current or arc-over'within the bushing 49 and externally of the tube 31, itis contemplatedy that the leads 42 and 43 of the secondary windingf4| of the insulating transformer may be passedthrough andfsealed in the wall of the insulating vbushing 49 to thus 'provide an oil tight receptacle thatmay be filled with an insulating 'oil or `other medium:

51. In'this figure of the drawing'thev primary windingf45 is shown as provided withan'electro'- static shield 60. This shield maybe Aoffan'x'r'accepted form and will functiony to prevent-any electrostatic discharge to the primary coil. y'The bottom ofthe insulating bushing 49 is shown'as closed by a plate 58, but it will be understood that this closure may be provided by any 'suitable means and may constitute a part of otherfappara-vv tus with which the insulating transformeris' used. In this instance the evacuated glas'sbulb `or envelope 31 is supported upon insulating blocks '59,. However, it will be understood that the`bulb`31 may be supported in many other ways. v"For example, it may be carried by shelf formingfbosses formed integrally upon the inside wallfof the bushing 49, or it may besuspended from 'the-plate 50 which supports the core 5I of the conventional transformer. As an additional safety measure,Y it will be understood that yif desired, the cores of the insulating transformers described'above lmay be grounded, as indicated in Figure 3. yIn 'the Acase of high frequencies, or other conditions'permitting, itis also conceivable that the'magnetic core This will 'i orm 'amecase `of extremely high potentialefit may also `be desirable to employ and connect two or `more of;

these insulating 'transformers `in series soies to ,l y

establish any numberfo'f stages of l trans formation and insulation. I

-Although'thefinvention has been .illustratedand yexplained in `detail in-conlunction'with aspecilc "application-*andas a current transformery forvhigh Ypotential alternating l cu-rrent systems, .it is not necessarily limited to such afield of-application. The inventionquitegenerally shows a novel means for inductivelycoupling and insulating two cir- Vcuitsthat operate at greatly'.dllerent potentials.

4It will also -be understood that the systems dcscrlbed canbe used to transmit direct current impulses from the. primary'tc the-secondary or vice versa, fand in this manner y.the-transformer here disclosed could be usedvas the insulated inductive c'oupling-meansshown anddescribed in U. S. Patent No. 2,301,765, issued November 10, 1942, to

Roy Wilkins.

Yscope of the appended claims are to be considered Las partof this invention.

Having thus described my invention, what I claim Vand desire to secure by Letters Patent is:

1. A current transformer for use on high po- -tentlal circuits, comprising an evacuated envelop-e having armagneticcore mounted therein andsurrounded rbye. vacuum, a primarywinding mounted inloose coupled magnetic relation vuporisaid. magnetic-core within said evacuated fenvelopeand 'adapted' to be excited by vthe line fcurrentwof avhigh potential circuit, anda sec 'ondary 'win'ding 'mounted' upon said Acore in close vcoupled inductive yrelation with Hsaid magnetic core, characterized. by theV fact that said primary -win'ding will be' electrically insulated from said v'magnetic core andk from saidV secondary winding-Y ssfsole'ly by .the levacuated space therebetween within said-evacuatedenvelope. l

.2. In-a current transformer for4 tappi-ng va high .a potential'v circuit, `lthe combination. of :an evacuated fsealablet container 1. ofv Vnon-conducting ma- "terial, laprimary! coil havingv relatively large turn forming'convblutionsfdisposed within said container *andfhaving f'extending .terminal ends adaptedfforconnection to 1a. high potential cirfcuit, atclosed magnetiecoi-ehaving one-leg extendingfcentrally' through andl in" loose coupled .-lrnagnetic relation with the; large turn forming convolutionst-of saidifprimary coilfand a secondaryrcil mounted in closecoupled magnetic relation-.upon 'another' leg "of said l'magnetic core,

lwhereby* saidprimary coillwill be electrically insulated.ffrom'said'closed magnetic core and said secondary coil by a vacuum.

*3; In a current transformer of the character cdescribed, the combination voi' an evacuated container, an electromagnetic core mounted within and supported by said container, afprimary windated space therebetween'.

4. A current transformer'for Obtainmgmetering and control current values of low ratio error from high potential power transmissioncircuits', the combination of a primary winding having large turn formingconvolutions adapted to be connected toa high potential circuit, a closed magnetic core having a portion extending through the large turn forming convolutions of said primary winding and y, in spaced loosely coupled magnetic relation therewith, a secondary winding disposed in spaced relation with said primary winding and wound in close coupled relationk about another portion of said closed magnetic core, and a sealed' and evacuated enclosure formingmeans completely surrounding and supportingsaid primary winding and said magnetic "core 'in spaced relation to each other, whereby said highV potential primary winding will be effectively insulated from said magnetic Vcore and said secondary windings by the evacuated space therebetween.

5. A current transformer for obtaining metering and control current values of 'low `ratio error fiom high potential power transmission circuits, the combination of a primary winding having large. turn forming convolutions adapted to be excited by a current at high potential, a close/d magnetic. core having a portion thereof extending through and in loosely coupled magnetic relation with the large turn forming convolutions of said primary winding, a secondary winding disposed inspaced relation with said primary v winding and wound 'in closecoupled magnetic re- V.lation upon another portion of said closed magnetic core, an evacuated enclosure forming means having terminal leads for said windings extend- I ing through opposite walls thereof and completely surrounding and supporting said primary Winding and said-magnetic core in spaced relation to each other, whereby said high potential primary winding will lbe eiectively insulated from said magnetic core and said secondary winding by an evacuated 'space therebetween, and a bushingsecondary windings.

like support containing a fluid insulating medium within which-said evacuated enclosure forming means is vsubmerged to prevent current creepage between the terminals of said prmaryand said AuGUs'r c.v scHwAGER. 

